The present invention relates to systems and methods for cylinder air charge estimation used in controlling an internal combustion engine.
Precise air/fuel ratio control is an important factor in reducing feed gas emissions, increasing fuel economy, and improving driveability. Current internal combustion engine designs use various temperature, pressure, and flow sensors in an attempt to precisely control the amount of air and fuel, and thus the air/fuel ratio, for each cylinder firing event. However, due to various sensor limitations such as response time and being located away from the combustion chamber of the cylinder, it is difficult to precisely measure and coordinate or synchronize the air and fuel quantities which are actually combusted in the cylinder. Acceptable control strategies have been developed to compensate for various sensor limitations under steady-state operating conditions. Effort is now being focused on improving these strategies to provide more accurate air/fuel ratio control during transient as well as steady-state operating conditions.
Electronically controlled throttle valve actuators have been used to improve transient air/fuel ratio control by providing increased control authority over airflow. By eliminating the mechanical linkage between an accelerator pedal and the throttle valve, the engine controller can control throttle valve position to deliver the proper airflow for current driver demand and operating conditions.
Airflow is typically measured using a mass airflow (MAF) sensor positioned upstream of the throttle valve. Intake air travels past the MAF sensor, through the throttle valve and into the intake manifold where it is distributed to a bank of cylinders. Intake air enters a cylinder upon the opening of one or more intake valves. Fuel may be mixed with the intake air prior to entering the cylinder or within the cylinder for direct injection applications. The response characteristics of current MAF sensors coupled with the delay time associated with throttle valve positioning, transit time of the air mass between the MAF sensor and the cylinder, and response time of the fuel injector, make it difficult to accurately determine the precise quantity of air and fuel in the cylinder.
Various prior art approaches have attempted to improve air/fuel ratio control and compensate for one or more of the above factors. For example, one approach attempts to synchronize throttle valve positioning commands and fuel injection commands in the crank-angle domain so that throttle valve movement is prohibited after air flow measurement. Another approach delays throttle valve movement to allow time for the fuel system to react. One strategy which provides a future estimate of cylinder air charge linearly extrapolates a current airflow measurement for a future fuel injection event. However, this method assumes air charge changes at a constant rate and does not compensate for airflow sensor filtering effects which lead to an attenuated and delayed response.
It is an object of the present invention to improve air/fuel ratio control using adaptive and observer-based controls to provide an estimate for future cylinder air charge during a future fuel injection event.
In carrying out the above object and other objects, features, and advantages of the present invention, a system and method for controlling an internal combustion engine having an electronically controlled airflow actuator, such as a throttle valve or intake/exhaust valves, include predicting position of the airflow actuator using an actuator model corresponding to a subsequent injection of fuel into the cylinder and estimating air charge in the cylinder for the subsequent injection of fuel based on the predicted position of the airflow actuator. In one embodiment, an airflow model is used to determine a future intake airflow based on the future position determined by the actuator model. A manifold filling model may then be used to provide the estimate for the future cylinder air charge with an appropriate amount of fuel scheduled to deliver a desired air/fuel ratio within the cylinder. The models, their associated parameters, and/or output values may be modified using measured values for mass airflow and throttle valve position.
The present invention includes a number of advantages relative to prior art approaches. For example, the present invention compensates for inherent sensor dynamics to produce air charge estimates based on actual airflow actuator position and/or motion. The present invention uses existing sensors to improve stability and prediction accuracy for both airflow actuator position and the resulting airflow. The present invention uses adaptation and learning to adjust model parameters and/or outputs and compensates for modeling inaccuracies. The improved air/fuel ratio control based on more accurate in-cylinder air charge determination may result in reductions in the size of catalyst which would otherwise be necessary to accommodate excursions from stoichiometry induced by transient control inaccuracies.